A Framework to Evaluate the Performance of Urban Rainwater Harvesting Systems Considering Water and Sanitation Utility Perspectives under Deep Uncertainties

Rainwater harvesting systems (RWHS) are supplementary to conventional water supplies, and assessing their potential advantages for the urban environment and impacts on the water and sanitation utilities (WSUs) is necessary for the development of public policies that promote their adoption. This study developed a methodology for assessing the potential water savings and respective economic impacts on WSUs in Brazil under a context of deep uncertainties and applied this method in a Brazilian city. Initially, the performance indicators water saved, benefit–cost ratio, and modified benefit–cost ratio were defined. Then, 14 public policies were defined to evaluate the impacts of RWHS for different user groups and tariff approaches. The uncertainty related to the rainfall regime and other deep uncertainty factors (water tariff, service cost per cubic meter, household units and discount rate) defined 1,000 states of the world, comprising an ensemble of 14,000 scenarios. The RWHS were evaluated using a water balance simulation. The implementation of RWHS in all the households generated a reduction in the total consumption of water greater than 41%. Implementation of RWHS for the lowest consumption ranges demonstrated rainwater utilization potential of over 29%, and the number of scenarios economically feasible for the WSU increased with RWHS implementation across all predefined policies. As such, the proposed novel framework for adaptive modeling of RWHS under deep uncertainty proved useful in evaluating water-saving and economic impacts on WSUs, and in highlighting the potential effects of different public policies for promoting RWHS in other urban areas.